1. Field of the Invention
The present invention relates to an inkjet printhead substrate for making a record on a record medium by ejecting ink by an inkjet process, a method of manufacturing the inkjet printhead substrate, and an inkjet printhead including the inkjet printhead substrate.
2. Description of the Related Art
In recent years, thermal inkjet printheads which can be driven with low power consumption and which have high reliability have been demanded. A thermal inkjet printhead (hereinafter also simply referred to as “inkjet printhead”) is mainly composed of a device substrate for printheads and a channel-forming member having an ink chamber and ink ejection ports communicating with the ink chamber. The device substrate is provided with a heat-generating resistor (electrothermal transducing portion) generating heat that is energy for bubbling ink to eject ink. The heat-generating resistor is provided with a protective layer for avoiding the contact with ink. An insulating layer is placed between the heat-generating resistor and a semiconductor substrate such as a silicon substrate. Reducing the thermal conductivity of the insulating layer, which is placed between the heat-generating resistor and the semiconductor substrate, is effective in driving the inkjet printhead with low power consumption. Hitherto, an insulating layer on a semiconductor substrate has been made of silicon oxide (hereinafter referred to as SiO). SiO has a thermal conductivity of 1.3 Wm−1K−1 and therefore cannot sufficiently prevent heat from escaping into the semiconductor substrate. This has hindered the reduction of power consumption. Therefore, an insulating layer with a thermal conductivity less than the thermal conductivity of SiO, that is, a heat storage layer is demanded.
When the thermal conductivity of the heat storage layer is low, heat generated from a heat-generating resistor is unlikely to escape toward a substrate through the heat storage layer, the temperature of a heat application portion which is placed on the heat-generating resistor and which is contacted with ink rises efficiently, and input energy necessary to bubble ink is small. As a result, a printhead capable of being driven with low power consumption can be obtained.
FIG. 5 shows a printhead disclosed in U.S. Pat. No. 7,390,078 (hereinafter referred to as “Patent Document”). In the printhead, an insulating layer 28, a heat storage layer (low-thermal diffusivity film) 32, a heat-generating resistive layer 26, a cover layer (conductive metal layer) 60, and a protective layer 30 are stacked on a semiconductor substrate 22 and the junction between the cover layer 60 and the heat-generating resistive layer 26 acts as a fluid ejector actuator 17. The insulating layer 28 is made of silicon oxide, silicon nitride, or the like. The heat storage layer 32 is made of the aerogel of a ceramic oxide such as silica, titania, or alumina. The heat storage layer 32 has a pore size of less than 100 nm and a low thermal conductivity of about 0.3 Wm−1K−1 to 1 Wm−1K−1. Therefore, the printhead can be driven with low power consumption.